Yankee type hoods are among the main elements in paper web drying processes and, specifically, a Yankee hood is an air distribution and drying system which operates at high temperatures. The hood is shaped to be installed over a portion of the circumferential surface of a rotatable drying cylinder. The moving web material to be dried travels over, and with, the portion of the rotating cylinder. The internal structure of the hood includes an air distribution system which conveys and directs hot, drying air onto the web travelling over the cylinder. A return air system in the hood utilizes space not occupied by the air distribution system and also includes the enveloping enclosure over the internal elements of the hood.
As described above, the hood is shaped for installation over the cylinder. The distance between the air distribution nozzles of the hood internals and the surface of the cylinder is referred to as the "impingement distance" and this is critical to a successful drying process. The shape or configuration of the hood near that distance is referred to as the hood profile. It will be appreciated that a good or fitting profile adjacent the cylinder ensures the best conditions for drying.